EXTRACTION OF CAFFEINE FROM TEA LEAVES

In this experiment the main objective was to determine the Caffeine content, by mass, of two brands of tea. During the experiment, the two brands of tea were boiled with 70ml of distilled water for 15 min. The mixture was cooled and put into the separating funnel followed by three washings of dichloromethane.

The mixture were dried with anhydrous sodium sulphateThe remaining substance was then evaporated until only white crystals remained, which were considered to be crude Caffeine.

The obtained products were dissolving in 5ml acetone followed by 6ml petroleum ether and then boiled to reduce the volume up to 3ml. The content was allowed to cool at room temperature. The formed precipitate was used to measure the melting temperature.The percentage yield was computed by getting theratio of the weight of the crude caffeine (residue) and weight of the tea leaves used. The percentage yield was 4.54% and the melting temperature was 227°C -230°C

INTRODUCTION OF THE EXPERIMENT.

The technique used to separate an organic compound from a mixture of compounds is called Extraction. Extraction process selectively dissolves one or more of the mixture compounds into a suitable solvent. The solution of these dissolved compounds is referred to as the Extract. Here the organic solvent dichloromethane is used to extract caffeine from an aqueous extract of tea leaves because caffeine is more soluble in dichloromethane (140 mg/ml) than it is in water (22 mg/ml).

However, the tannins that are slightly soluble in dichloromethane can be eliminated by converting it to their salts (phenolic anions by adding sodium carbonate)(tannins are phenolic compounds of high molecular weight and being acidic in nature can be converted to salts by deprotonating of the -OH group) which remain in the water.

Caffeine constitutes approximately to3%-5% of tea and coffee leaves. Caffeine is an alkaloid, and, more specifically, a member of the methylxanthines. Thus, Caffeine is closely related to theophylline and theobromine.In Humans, Caffeine acts to stimulate the heart, central nervous system, and the respiratory system. Blood pressure is increased by its use, since heart rate is increased, as is contraction force and volume output.

Equipment and Materials:

· Large Beaker

· Dichloromethane

· Distilled Water

· Analytical balance

· Hot Plate

· Ice water bath

· 100ml Graduated Cylinder

· separatory funnel

OBSERVATIONS.

The following were the observed during the experiment;

a) Formation of solid white crystals of caffeine during evaporation processes for Dichloromethane and Acetone.

b) Formation of two layer of liquid in the separating funnel during isolation of dissolved caffeine in Dichloromethane from aqueous layer.

c) The white crystals of pure caffeine were observed to melt from 287 ^oC – 230 ^oC.

RAW DATA.

The following were the raw data of the experiment;

· Weight of Tea leaves + Tea bags=4.4682g

· Weight of 2 empty tea bags=0.26g

· Weight of tea leaves=4.2082g

· Weight of small empty conical flask=63.9778g

· Weight of small empty conical flask + Crude Caffeine=64.3705g

· Weight of small empty conical flask + Pure Caffeine=64.1692g

· Melting temperature of pure Caffeine=227 ^oC – 230 ^oC.

CALCULATION.

Calculation of the percentage yield is as follows;

· Weight of tea leaves=4.2082g

· From the raw data the weight of crude caffeine

=64.3705g-63.9778g

=0.3927g

Therefore weight of crude caffeine=0.3927g

· Weight of pure caffeine

=64.1692g-63.9778g

=0.1914g

Therefore weight of pure caffeine=0.1914g

Percentage of caffeine yield= (Weight pure caffeine)/(weight tea leaves) x 100%

=0.1914g/4.2082g x 100%

= 4.54%.

Percentage of caffeine yield=4.54%.

RESULTS

The following were the results of the experiment

i. Percentage of caffeine yield=4.54%.

ii. The melting temperature of pure caffeine=227 ^oC – 230 ^oC.

DISCUSSION AND ANALYSIS.

Ø By comparing the theoretical and experimental results shows that the values i.e. the theoretical percentage yield is approximately to 3%-5%where as for the experimental yield is4.54%which is in the same range as theoretical values. But for the theoretical melting temperature of pure caffeine range from (227^oC–228^oC)which is somehow differ for the experimental melting temperature(227 ^oC – 230^oC).

· These differences may be due to the uncertainty in measurement(errors), and these can be

§ Recording the observation wrongly especially during the measuring the melting temperature.

§ Entering the wrong observation in measurement.

CONCLUSSION

In consideration of the numerous sources of error, this experiment has been a success. Pure, or mostly pure, Caffeine crystals have been isolated from tea leaves and weighed. This value was similar to the accepted Caffeine content of tea, thus the results supported the original hypothesis.

But for melting temperature of caffeine those differences maybe resulted from uncertainty in measurement(errors) as explained above in discussion, and those errors can be avoidable when careful observation is undertaken and other precaution about sources of error is caring out.

QUESTIONS

1. Suggest other ways to isolate the caffeine from tea leaves.

Answer

The following are other ways of isolating caffeine from Tea leaves

a) Carbon dioxide (CO₂)process

This process is technically known as supercritical fluid extractionwhere by decaffeinated tea is essentially “pressure cooked” with this naturally occurring gas. At high pressures and high temperatures, carbon dioxide reaches a supercritical state. The CO₂ becomes a solvent with its small, nonpolar molecules attracting the small caffeine molecules. Since flavor molecules are larger, they remain intact, which is why this process retains the flavor of the tea the best.

Direct method

In the direct method, the tea leaves are first steamed for 30 minutes and then repeatedly rinsed with either dichloromethane or ethyl acetate for about 10 hours. The solvent is then drained away and the leaves steamed for an additional 10 hours to remove residual solvent. Sometimes tea leaves that are decaffeinated using ethyl acetate are referred to as naturally processed because ethyl acetate can be derived from various fruits or vegetables, but because of the impracticality of gathering natural ethyl acetate, the ethyl acetate used for decaffeination is synthetic.

Water extraction

Hot water extracts both flavor ingredients and caffeine from green coffee beans. If the extract is passed through activated charcoal, most of the caffeine is removed. Soaking the original beans in the decaffeinated extract then restores most of their flavor.

d Indirect method

In the indirect method, tea leaves are first soaked in hot water for several hours, in essence making a strong pot of coffee. Then the leaves are removed and either dichloromethane or ethyl acetate is used to extract the caffeine from the water. As in other methods, the caffeine can then be separated from the organic solvent by simple evaporation. The same water is recycled through this two-step process with new batches of tea leaves. An equilibrium is reached after several cycles, wherein the water and the tea leaves have a similar composition except for the caffeine. After this point, the caffeine is the only material removed from the tea leaves so no tea strength or other flavorings are lost. Because water is used in the initial phase of this process, sometimes indirect method decaffeination is referred to as "water-processed".

e Methylene chloridedecaffeination

Is a process by which the molecules of caffeine bond to molecules of methylene chloride. Caffeine is removed either by (1) directly soaking the tea in methylene chloride or (2) indirectly soaking the water (used to remove the caffeine) in methylene chloride and then returning the water to the tea for reabsorption of flavors and oils.

2. Why sodium carbonate is added during the boiling of tea leaves.

Answer

The sodium carbonate acts as a base - you could use sodium hydroxide instead. When you boil tea leaves tannins dissolve in the water as well as the caffeine. If you do not use a base the tannins will also be extracted into the solvent (i.e. Dichloro Methane) used in the subsequent extraction. The base converts the tannins into their sodium salts - being ionic these salts are not soluble in solvents like Dichloro Methane so remain in the aqueous layer during extraction. This allows purer caffeine to be extracted.